U.S. Pat. No. 5,057,710 teaches electret materials comprising hindered amines, nitrogen containing hindered phenols or metal-containing hindered phenols.
U.S. Pat. No. 5,556,618 discloses antibacterial electet materials.
U.S. Pat. No. 6,123,752 teaches high efficiency filter medium containing a performance enhancing additive.
U.S. Pat. No. 6,743,464 teaches a method of making electrets through vapor condensation.
U.S. Pat. No. 6,969,484 discloses a method of making electret.
U.S. published app. No. 2003/0216494 teaches hindered hydroxylamine ester compounds.